Coccidia were found in a patient suffering from malabsorption syndrome. In addition, immunologic investigation showed combined humoral and cellular immunodeficiency. Treatment with metronidazole induced the disappearance of coccidia from the stool and clinical remission. Six months later, the patient was seen with acute lymphoproliferative disease and died thereafter. The possible relationship between malabsorption, immunodeficiency, coccidiosis, metronidazole, and malignancy is reviewed.